Process for dehydrating vapor mixtures containing acetic anhydride and water



Patented July 21, 1931 UNITED STATES PATENT OFFICE- FBANZ SOHLEICHER, OI 'WIESDORF-ON-THE-BHINE, GEORG SCHWAEBEL, OF LEVER- KUSEN-ON-THE-RHINE, AND KURT BRIESEWITZ, OF COLOGNE-DEUTZ. GERMANY, ASSIGNORS TO I. G. FARBENINDUSTRIE AKTIENGESELLSCHAIFT, OF FRANKFURT- ON-THE-MAIN, GERMANY, A CORPORATION OF GERMANY PROCESS FOR DEHYDRATING VAPOR MIXTURES CONTAINING ACETIC ANHYDRIDE AND WATER No Drawing. Application filed January 26, 1928, Serial No. 249,762, and in Germany February 11, 1927.

water, but simultaneously reduce the vapour tension of the acetic anhydride. The working of the process is effected by the use of the customary separating columns in which the organic solvent employed as the carrier for the water-vapour is not onl introduced from the top of the column, ut also simultaneously from below. The process may also be. carried out by using the solvents in the vaporized state, but in that case care should be taken that the temperature of the vapors of the solvents entering the column is not too high, preferably not higher thanv about 100 C. Furthermorethe separating column may be extended by placing at the upper end a dephlegmator in which case the or anic solvents are forced into the separating co umn only from below.

The quantity of the organic solvent used may be varied within the widest limits, and in carryin out our process anyone skilled in the art W1 1 readily find a suitable ratio of solvent to the mixture of water, acetic anhydride and acetic acid. When continuously carrying out our process, we prefer to use at least an amount of solvent equal in volume to -one half the volume of the initial acetic acid used. I

A vapor mixture of acetic anhydride, acetic acid and water, as contemplated to be used in our new process is, as is known, obtained by the pyrogenic decomposition of aceticacid. As the most valuable product, the

acetic anhydride, is very easily saponified again by the admixed water with the reformation of acetic acid, it becomes necessary to remove the water from the reaction product in such a manner, that the yield of acetic anhydride is not prejudiced.

The new process can be carried out in a separating column of the customary type, in which the still super-heated vapours of acetic anhydride, acetic acid and water are rinsed from above with an indifferent solvent boiling at about the boiling point of water, which means, between about 80 C. and 110 C., such as benzene, toluene,- chloroform, ethy lene chloride, trichloroethylene and the like, in such a manner and with such quantities that substantially only water distils over with the said solvent or a correspondin mixture thereof, while the acetic anhydride and the bulk of the acetic acid condense with a small quantity of the respective solvent, sub- 'stantially free from water, and run off below.

Mixtures of solvents can be employed with especial advantage, in which one constituent,

as stated above, 0 7 rates as a carrier for the water vapour, while the other constituent, a

solvent having a boiling point hi her than.

acetic anh ride, say, between a out 180 and 250 such as ortho-dichlorobenzene, uinoline, quinaldine and the like, reduces t e vapour tension of the acetic anhydride.

The action of the solvent or of the mixture of solvents trickling down the separating column can likewise be produced by the use of a dephlegmator, in which case the solvent or mixed solvents are forced into the separating column from below.

By way of example a separating column of the customary construction is employed, in which a readily volatile solvent, for example, benzene or a mixture of solvents, for example a-mixture of benzene and dichlorobenzene or of benzene and quinoline is caused to trickle down from above. In this connection it is advantageous also to inject into the separating column from below a current of benzene, toluene, or the like. Or, a separating column may be used, which has been extended by having placed at its upper e1. a dephlegmator. The workingof the process is then effected by injecting at the lower end, of the column a readily volatile solvent, for example, trichloro-ethylene or a mixture of readily volatile solvents, for example, benzene and trichloroethylene.

The anh dride condenses in a suitably heated recelver, the temperature of which is adjusted to correspond. to the nature and quantity ofthe solvents trickling down the column. The fractionation of the acetic anhydride mixture can then proceed either continually or intermittently,

In all these cases, the yield of anhydride, as ascertained by sampling from the column, is found to be substantially quantitative in the receiver, while the water distils over completely with the readily volatile solvent.

We claim: v

1. In the process for the dehydration of a vapor mixture containing acetic anh dride, acetic acid and water, the steps which comprise adding to the vapor nuxture at least one organic solvent indliferent to acetic anhydride and having a boiling point of about that of water and removing the water together with said solvent by subjecting the vapor mixture to fractional distillation.

2. In the process for the dehydration of a vapor mixture containing acetic anhydride, I

acetic acid and water, the ste s whic comprise addingto the'va or mlxturc at least one organic solvent indifferent to acetic anhgdride and having a boiling point between a out and 110 0., an removin the water together with said solvent by su ectmg the vapor mixture to fractional dlstillation;

3. In the process for the dehydration of a vapor mixture containing acetic anh dride,

acetic acid and water, the ste s whic com-r prise adding to the vapor mixture at least one solvent of the group consisting of henzene, toluene, chloroform, ethylene chloride and trichloroeth lene, and removing) the water together w1th said solvent by su 'ecting the vapor mixture-to fractional distillation. '7 a 4. In the process for the dehydration of a vapor mixture containing acetic anhidride, acetic acid and water, the steps whic comprise adding to the va or mixture an organic solvent having a boiling point of about that of water and another organic solvent having prise adding to the vapor mixture an organicv solvent havmga boiling point between about 80 and 110 C. and another solvent havin a boiling point between180 and250 C. bot solvents being indifferent to acetic anhydride,

and removing the water together with the.

' solvent having a boiling point of about that of waterby sub'ecting the vapor mixture to fractional disti ation.

In testimony whereof we have hereunto set our hands.

FRANZ SOHLEICHER. GEORG 'SOHWAEBEL. KURT BRIESEWITZ. 

